1. Field of the Invention
The present invention relates generally to acrylated chlorinated rubber, a method for making acrylated chlorinated rubber, and environmentally friendly photocurable rubber coatings comprising acrylated chlorinated rubber.
2. Background
Chlorination of cis-polyisoprene is a well established industrial process to produce chlorinated rubber. See, e.g., British Patent No. 381,038 (1859) and U.S. Pat. No. 1,234,381 (1912). Chlorinated rubber has long been used in surface coatings to provide abrasion resistance, chemical and water resistance, flame retardance, durability and toughness. It is one of the best anticorrosive binders widely used in hostile environments such as marine coatings, swimming pool coatings and traffic paints.
Chlorinated rubber, however, is a non-convertible or nonreactive binder. That is, chlorinated rubber does not alter its structure or react with other ingredients in the coating composition during curing. Thus its applications have been limited to solvent based coatings of high volatile organic content (xe2x80x9cVOCxe2x80x9d). Such coatings are cured exclusively by solvent evaporation, which causes air pollution. Although still allowed, high VOC coatings have been largely replaced by new technologies such as water borne, high solids, and powder coatings in response to stringent legislative regulatory requirements.
Chlorinated rubber coatings suffer from a further problem of poor solvent resistance due to lack of crosslinking between the chlorinated rubber binder and the solvents or diluents used in the coating compositions.
These problems associated with chlorinated rubber coatings have existed since chlorinated rubber was first utilized in the coatings industry approximately fifty years ago. They have become more serious since the Environmental Protection Agency began in 1967 to regulate VOC levels in coatings and they will become even more serious as more and more stringent environmental regulations take effect in the future.
A need therefore exists for a functionalized chlorinated rubber that will act as a convertible binder, i.e., a reactive binder, in coating applications, thereby reducing VOC levels, and that will impart improved solvent resistance to coating formulations.
Functionalization, or chemical modification, of chlorinated rubber has been a topic of extensive studies in recent years. Most of the studies have used direct modifications of chlorinated rubber, such as free radical initialized graft copolymerization with a variety of functional acrylate or styrene monomers. Direct modifications of chlorinated rubber are limited, however, due to its chemical inertness and thermal instability. Moreover, unwanted side reactions such as polycondensation and elimination are unavoidable.
Hydroxylation of rubber via. saponification of the reaction adduct of rubber and haloacetic acids has been recently reported. Y. H. Kim and A. Pandya, Macromolecules, 24, 6505-11 (1991). However, the commercial value of the product, partially hydroxylated rubber, also known as hydroxyrubber, was not assessed, nor were coating applications mentioned, since hydroxyrubber does not possess properties necessary for coating grade materials.
It has now been discovered that acrylated chlorinated rubber provides outstanding properties in coating applications and makes possible the formulation of 100% solids photocurable rubber coatings.
In accordance with one aspect of the present invention, there is provided a composition comprising acrylated chlorinated hydroxyrubber.
In accordance with another aspect of the present invention there is provided a method for making acrylated chlorinated rubber. The method comprises reacting chlorinated hydroxyrubber and acryloyl chloride with triethylamine as a catalyst. The rubber which can be utilized includes masticated natural rubber, masticated synthetic rubber, low molecular weight natural rubber, and low molecular weight guayule rubber (xe2x80x9cLMWGRxe2x80x9d). The hydroxyl and chlorine content of the chlorinated hydroxyrubber can be altered by varying the reaction times. No unwanted side reactions have been noted.
In accordance with yet another aspect of the present invention, there are a method of making and formulations for photocurable rubber coatings comprising acrylated chlorinated rubber.
Acrylated chlorinated rubber prepared by the method of the present invention provides improved properties when compared to conventional chlorinated rubber and when compared to chlorinated hydroxyrubber. Acrylated chlorinated rubber is a convertible binder, and, thus, allows crosslinkable reactive solvents or diluents to be utilized in coatings formulations, so that the solids content of the coatings will be increased. Because acrylated chlorinated rubber can be formulated into 100% solids coatings and cured by radiation induced free radical polymerization, the reactive solvents or diluents become part of the coating and, therefore, cause no air pollution. Acrylated chlorinated rubber also imparts excellent solvent resistance to coatings formulations because of the crosslinking of reactive diluents and the functional groups of the chlorinated rubber. In addition, the incorporation of acrylated chlorinated rubber in coatings imparts superior adhesion, sanding, and hardness properties.
Acrylated chlorinated rubber can be used in coatings, printing inks and adhesives. Photocurable acrylated chlorinated rubber coatings typically comprise a functionalized prepolymer, reactive diluents, photoinitiators and various additives. Formulation examples and coating properties of 100% solids coatings comprising acrylated chlorinated rubber are provided.
Other features and advantages of the present invention will become apparent from the following detailed description, which is given by way of illustration only.